Heat pump



M. C. REESE HEAT PUMP Sept. 5, 1961 Filed June 5, 1959 2 Sheets-Sheet lINVENTOR #Z C Feed&

BY J

ATTORNEY Sept. 5, 1961 M. c. REESE & 83

HEAT PUMP Filed June 5, 1959 2 Sheets-Sheet 2 .Syl 0. ,4 Call.

0. co IL INVENTOR #Z 6? flee e ATTORNEY ie a This invention relates toheating and cooling apparatus and particularly to a heat pump having amultiple outside air coil arrangement and an automatic alternatingde-icing system formed as an inherent part of the pump.

Heat pumps have come into considerable use of late years and the numberof installations is rapidly increasing.

The heat pump it should be borne in mind is a desi'- able device becauseit provides the means for air conditioning a home for example in thesummer and heating in the Winter with installation of a single type ofequipment. Heating and air conditioning of homes are not new is mostareas and in most known prior installations a separate furnace and aseparate cooling system are employed with one being operable in theWinter and the other in the summer. The obvious advantage of having asingle unit which performs both functions is apparent in so far as thefirst cost of installation is used. There is further a sought foradvantage to public utilities corn panies in equalizing the summer andWinter power loads. Air conditioning has generally put summer power loadconsiderably out of line with Winter load. Heat pumps were considered ananswer to this problem.

However, the prior installations known in the art of the single outsideair coil type utilize heating strips or strip heaters as a means ofsupplementary heat in the Winter and from time to time rely on theheaters entirely when the outside air temperature is low enough to causeconsiderable icing on the outside air coil.

In fact Very often this strip heater load becomes a considerable portionof the power consumed and in so far as the power company is concernedresults in a peak load in the Winter instead of the summer. Whereaspower companies as indicated above have been promoting the sale of heatpumps in order to balance their heavy air conditioning loads in thesummer. in other words, to have a more uniform load the year round andthus make the installation and operation of generator equipment moreeconom'cal. e

One factor in this is that the refrigeration equipment Capacity insingle coil systems have all heretofore been designed and sized tohandle the cooling load only, so when a system of this type is used,electric heater strips of sutficient capacity to handle the maximumheating load are a necessity. These strips are usually controlled sothat they can be energized in three steps of approximately 33 /3 percenteach. One or two steps are used as supplementary heat while the heatpump is Operating and all the strips are used while the coil is beingde-iced.

In most sections of the country if three tons of summer air conditioningequipment is needed for summer cooling approximately three kw. is usedfor cooling. The heating kw. used to heat the same building will beapproximately 10 kw. while the single coil is being de-iced andapproximately 5 kw. as supplementary heat while the heat pump isOperating. Bear in mind while the latter condition eXists that the threekw. required to ope-rate the refrigeration equipment is also being usedmaking a minimum of 8 kw. approximately whereas my heat pump can do thesame job with a maximum of five kw. All strip heaters and therefrigeration equipment on conventonal heat pumps will be in operationat the same time for a big percentage of the time using a total ofapproximately 13 kw. as compared to five kw. with my heat pump.

Accordingly an object of this invention is to provide a means ofde-icing heat exchangers such as evaporators on the outside air coilsWhile maintaining adequate heat te %i 2398310 Patented Sept. 5, 1961entirely from an outside air source wherein inoreased power load forthese purposes will be less than one-third the increase Compared withknown equipment of a comparable size where auxiliary electric heaterstrips are used.

Yet a further object of the invention is to provide a heat pump havingself contained de-icing means and wherein no equipment other than theheat pump itself is needed. According to the instant invention two ormore if desired outside air coils are necessary but the strip heaterinstallations previously required and their controls are not necessary.

Still another object of the invention is to provide a simplified controlsystem for automatically controlling the operation of the improvementwhich provides the automatic de-icer cycles.

Still a further object of the invention is to provide an automaticde-icer without the use of electical strip heaters or any auxiliary heatsource and to furnish a continuous uninterrupted heat supply from theoutside air alone.

A still further object of the invention is to provide equipment whichwill start either on heating or cooling without manual change overswitches or attention of any i kind. r

A further object of the invention is to provide a heat pump wherein allmotors and Controls except inside fan motors are de-energized when thethermostat is satisfied.

Another object of the invention is to provide heat pump equipment whichhas automatic self contained de-icing means and provision for recoveringheat used with the de-icng rather than permitting the loss of this heatto the outside air.

'These and other objects and advantages will become apparent from thefollowing description and the accompanying drawings wherein:

FIGURE 1 is a 'top plan View of a heat pump constructed in accordancewith the invention installed in a building.

FIGURE 2 -is a side elevational View.

FIGURE 3 is a front elevational view.

FIGURE 4 is a schematic diagram of the heat pump.

FIGURE 5 is a schematic diagram of the electrical system employed withthe pump.

FIGURB 6 is a side elevational View similar to that of FIGURE 2 butshowing the installation of a split type unit with the compressor,receiver and heat exchanger located outside of the building butconnected, by suitable piping to a heat exchanger located within thebuilding.

Referring now in particular to FIGURES 1, 2 and 3: A heat pumpconstructed in accordance with the instant invention comprises acompressor 10, a receiver 12, and an inside air coil 14, an outside aircoil No. l designated by the numeral 16, and an outside air coil No. 2designated by the numeral Ll. According to the invention the heat pumpis provided as a neat compact unit within a housing 20. The housing hasa partition 22 co Operating with side walls 24 and 26 and top and bottomwalls 28 and 30 to divide the housing into two Compartments. The outercompartment 32 containsthe outside air coils and the inner compartment34 contains the ini side air coil and the compressor and receiver. Theair coils are provided with suitable enclosures and each are providedwith fan means such as 36, 38 and 40. The housing comprises anotherpartition 42. This joins partition 22 and top and bottom walls 28 and 30to divide the outer compartment 32 into two chambers 44 and 46. Each ofthe air coils is mounted in one of the chambers and extends completelythereacross adjacent the upper end. It is to be understood that morethan one inside air coil or heat exchanger may be employed as well asmore than two outside air coils or heat exchangers, as well as several 3compressors, depending upon the size of the building or area that is tobe either heated or cooled.

Suitable baling means around the air coils and the fan housings provide'for direction of the air over the coils. Each of the fans illustratedare squirrel cage type blowers although any type can be used. The innerfan 36 is provided with a plenum 48 and can be connected to Conduit 50to take in air from the area being heated or cooled. The sheet metalingapplied to the inside coil 14 also directs the air from this coil andfrom the fan to an inner plenum 52 which is connected to the variousleadotfs to different areas as is well known in the art.

The two outside coil fans 38 and 40 have their intakes within theirrespective housing chambers 44 and 46. These chambers have lower inlets54 and 56 protected by suitable removable insect screening such as 58and adapted to be extended through the outside wall 60 of a building,for example. The outlets of the fans are connected by suitable sheetmetal work so as to force the air from the fans over the outside aircoils through the two outlets or discharges 62 and 64. These are eachprovided With air louvers 66 which are of a known type whichautomatically close when the fans shut down and open when the fansstart.

A sail switch 68 is located in the intake portion of the outside aircoil chamber 46. The sail switch is exposed to the force of the airbeing sucked in by the fan 40 and adapted to have its contacts opened orclosed in accordance with the amount of air passing over the surface ofthe heat exchanger or air coil located within the compartment 46. Theswitch is normally closed so that when the air flow starts this switchwill open. `If the weather is mild and the heating load is low, no icewill form on the 'heat exchanger or outside air coil 18 located withincompartment 46 and the sail switch contacts will remain open allowingthe heat exchangers outside air coil 18 to continue in operation. Whenthe outside air temperature drops to a point whereby ice forms on theheat exchanger or outside air coil 18, the flow of air through said beatexchanger is consequently reduced, the'eby causing the sail switch toclose its contacts which eventually results in the fan associated withthe heat exchanger or outside air coil 18 being stopped, which actionperrnts or causes the heat exchanger and/ or outside air coil 16 to bebrought into operation While at the i same time, through the actuationof various valves, enables the heat to be delivered to the heatexchanger or outside air coil 18 for the purpose of de-icing.

It is apparent from FIGURES 1, 2 and 3 that the heat purnp package isadapted to be installed adjacent the outv side wall of the building orwith ducts to the outside air ntakes and discharges flush and the insideintakes and discharges being adapted to be connected to the air conduitsystem of the building.

FIGURE 6 illustrates an installation of a package type unit where thecompressor, receiver and outside air coils are mounted in a unit 70placed at any desirable distance from the building or adjacent to it.Suitable refrgerant piping 72 extends from this package unit into theinterier of the area to be heated or cooled. inside air coils 74 aremounted wherever desired and provided With fan and Conduit structuresuch as 36, 48, 50 and 52 as will be apparent to those skilled in theart.

Referring now in particular to FIGURE 4:

The compressor, receiver and outside and inside air coils arenterconnected by known types of refrigerant and heat pump piping.

The compressor is schematically indicated to have a discharge side 76and an intake or suction side 78. Two lines 80 and 82 lead from thedischarge and similarly two lines 84 and 85 lead up to the suction.Lines 80 and 84 are connected to a common header 86 and lines 82. and 85connect to a common header 88. Valves 90, 92, 94 and 96 are positionedin the lines intermediate the suetion and discharge connections of thecompressor and the headers 86 and 88. The compressor of course runscontinuously in one direction. It is not reversible. Through means ofthe lines, header and valve structure disclosed, however, it is possibleto direct the discharge into either one of the headers 86 and 88, andlikewise to cause either one of these headers to become a suction header(alternately). Thus by closing valve 90 and opening valve 92 and closingvalve 96 and opening valve 94 the compressors will suck from header 86and discharge into header 88. Conversely When the valve 92 is closed,the valve 90 is opened, and the valve 96 is opened while the valve 94 isclosed, header 88 will become the suction side and header 86 will becomethe discharge side.

Header 88 leads directly to the inside coil 14 and header 86 leads tothe outside air coils. The latter header 86 is split into lines 91 and93 leading to coils No. 1 and No. 2, respectively. The solenoid valve 1Ais interposed in line 91 between it and its coil and solenoid valve 2Ais interposed in line 93 between it and coil No. 2. Intermediate thevalves and their respective coils there is a cross conneetng line whichconnects the two coils and is parallel to lines 91 and 93. A three-wayvalve designated S.V.4 is interposed in this line 95. The valve SiV.4 isconnected to a third line 98. Line 98 has interposed in it a solenoidvalve S.V.S. Like the other solenoid valves this is designated by theinitials S.V. The threeway valve 97 is adapted to connect either side ofthe line 95 to the line 98 and shut off the other side. Thus lines 95Aand 98 are connected while line 95B is shut oti, or line 95B isconnected to line 98 while line 95A is disconnected from line 98.

The opposte sides of the coils 16 and 18 are connected by lines 100 and102 to receiver 12. similarly inside air coil 14 is connected by line104 to receiver 12. Each of these lines are joined and each has its owncheck valve 103. Manual valve 106 is interposed in the common line. Thisleads to the top of the receiver. All the coils have duplicating linesleading from the bottom of the receiver. These lines are designated bynumerals 108, 110 and 112. Each of these lines has interposed thereinsolenoid valves designated as solenoid valve 1 in the line leading tocoil 1, solenoid valve 2 leading to coil 2, and solenoid valve 3 leadingto inside air coil 14. These lines are all joined and have a manualshuto valve 114 in the joined lines. Further each of these lines haveinterposed therein a thermal expansion metering valve as known in theart. Each is desgnated by T.E.

Referring now to FIGURE 5 The control circuit comprises four relaysdesignated as RI, R2, R3 and R4. Their coils are represented by circlesbeneath their numeral designations. The thermostatic control means forheating comprises the contacts whereas the cooling therrnostatic controlmeans comprises the paired contacts 122 and 124. These are embodied insuitable thermostats not shown on the drawings but can obviously be ofknown types.

The power leads 126 and 128 are connected through suitable protectivedevices 130 directly to the inside air fan by lines 132. Transformer 134having a 24 volt secondary is connected across the lines 132. ThisSupplies the current for the relay coils and the thermostatic contactshereinafter described. Leads 126 and 128 are directly connected to otherportions of the wiring dagram and particularly to the contacts of thevarious relays and to the valve solenoids. The latter have theirOperating coils designed to be operated by the main power source whichin this nstance is selected to be at 115 volts.

The coil of relay Rl is connected across the secondary of the 24 volttransfer-mer in series' with the thermostaic heating contacts 120. Thelatter are normally open. The Operating coil for relay R3 is similarlyconnected. In other words, it is parallel with the coil of relay Rl. Thecoil of relay RS is also connected in series with the secondary of thetransformer and normally opened contacts of the cooling thermostat 124.

The compressor is controlled by a coil operate (solenoid) switch thecoil of which is indicated by the numeral 136. This coil is connected tothe transformer in parallel with the relay coil RS both in itsconnection to the contacts 120 and its connection to contacts 124. Thecompressor solenoid is in series with the overload and high-low cutouts138 and 139. The coil of relay R2 is connected directly in series withthe secondary of the transformer `and the normally open contacts 122 ofthe cooling therrnostat. The coil of relay R4 is parallel with the relaycoil R2. The relay coil of relay RI is in series with the switch 68which is the sail switch positioned in the chamber 46.

The relay `1 has three sets of contacts RlA, RlB and RlC. RlA arenormally open, R1B are normally closed, and R1C'are normally open.Contacts RIA have in series with them coil S.V.1 of the solenoid valveS.V.l which is normally closed. This coil is further in series with therelay contacts R2C. Contacts R2C are controlled by the relay R2 asdescribed below. A coil 140 of a solenoid for Operating the controlswitch for the outside air fan No. 1, which is also desgnated by numeral38, is also v in series with the relay contacts RlA and an adjustabletime delay device 141. The adjustable time delay device can be anydevice that is satisfactory for operation on 115 volts or any otherselected voltage for the control circuit. It does not have to beoperated on 115 volts.

The following additional solenoid coils are also in series with therelaycontacts RlA, and relay contacts R4B and R4A, and in parallel witheach other: The operation coil S.V.1A of solenoid valve 1A; theOperating coil S.V. 2A of solenoid valve ZA; the Operating coil S.V.S ofsolenoid valve 5; the Operating coil S.V.3 of solenoid valve 3; theOperating coil S.V.7 of solenoid valve 7, and the Operating coil S.V.Sof solenoid valve 8. These coils will be placed in parallel with S.V.1and 140 whenever R4A and R4B are closed. S.V.1 is also in parallel withR4A and R4B and will be energized when R1A closes even though R4A andR4B are open.

The relay R2 has in addition to contacts RZE, normally open contactsR2A; normally closed contacts RZB, normally closed contacts RZC; andnormally closed contacts' RZD. Contacts R2A, which are normally open,are in parallel with the contacts R1A and in series with all the coilsthat are in series With R1A. Contacts RZB are normally closed andnormally connect to the parallel connected coils of solenoid valves 6and 9.

The normally closed contacts R1B are in series With the contacts RZD andthe coil S.V.Z of solenoid valve 2. The coil S.V.2 of solenoid valve 2and contacts RZD are in parallel with the coils S.V.ZA of solenoid valveRzA and the coil S.V.4 of solenoid valve 4. Thus the latter two coilsare in series with the contacts RIB.

Contacts RlC are in series with the time delay motor 144. The motor 144has' contacts 145 which are in turn in series with the normally closedcontacts RZE, an adjustable thermal time delay device 146 and the coil142. Coil 142 is the Operating coil for the switch for outside air fan40 which is the fan for outside air coil No. 2. Thus, with respect tothe latter coil, contacts RZE, 145 and delay device 146 are in parallelwith the contacts ZA and R4A and also with RIA and R4B. It should benoted that' coil 142 will also be placed in series with contacts R1Awhen the contacts R4B closes.

All valves of the described coils are normally closed V with theeXception of valve 5. This is a normally open valve, and energization ofthe coil of this valve serves to close it. Whereas the energization ofthe coils of all the other valves except S.V.4 serves to open thecorresponding valves. Solenoid operated valve 4 is normally closed, butit is normally closed only to outside air coil or heat exchanger No. 1.When the coil of valve 4 is energized the three-way valve closes to coilNo. 2 and opens to coil No. l. The valve remains open to line '98 at alltimes.

Relay 4 has a pair of contacts, described above. Relay trolled by theother relays, the solenoid valve coils, the r outside air fan switchesand the time delay device. All of these are deenergized when the coil R3is deenergized'.

OPERATION H eat'ng It will be noted from the circuit that no controlsfor the inside air fan are shown. It is normally Operating whenever thesystem is in operation. It can be controlled by separate thermostaticmeans or manually controlled, as is well known in heating and cooling.However, this forms no part of .the instant invention. Now assuming thatthe inside fan is continuously running and the thermostat calls forheat. This closes the contacts which are the heating thermostaticcontacts. This in turn energizes the coils of relays RI and R3 andcompressor switch coil 136. This starts the compressor and energizes theportion of the control circuit connected directly to the 115 volt line.When RI operates contacts R1A close, R1B open, and RlC close. Whencontacts RlA close they place the coil of the outside air fan 1 and thecoils of valves S.V.l and S.V.1A across the line, opening the ports inthese valves. The thermal time delay 141 delays the star-t of the fantfor the heat exchanger or outside air coil No. l for a few seconds toallow refrigeration equipment to reclaim part of the heat used inde-icing the heat eX- changer or outside air coil No. 1 rather thandissipate this heat to the outside air.

The energization of relay Rl also closes contacts R1C, starting timedelay clock 144 and immediately opening T.D. contacts 145 through theclock mechanism while also opening contacts R1B and thus de-ener izingand closing the ports in S.V.2 and S.V.2A, also de-energizing the 3- wayvalve S.V.4, thus closing its port to the outside air coil No. 1 line 98and line 9513, and opening its port to outside air coil No. 2, line 98and line 95A S.V.S is normally open and thus remains open during theheating cycle, thereby allowing hot gas to travel from the high pressureside of the system to the outside air coil being de-iced as beingselected or determined by contacts RllB. The port in S.V.4 to which line*98 is connected is continuously open.

The result of this is that valves S.V.l and S.V.1A open, fan No. 1 (38)starts running and time delay clock motor 144 starts running. Solenoidvalves 6 and 9 are opened while valves 7 and %remain closed. The heatingunit runs in this condition with the outside `air coil No. 1 picking upheat while the outside air coil No. 2 is being de-iced until contacts145 are closed by clock motor 144. When that occurs adjustable thermaltime delay 146 will be energized and after a few seconds delay OA fanNo. 2 (142) will start to operate. The adjustable thermal tirne delays146 and 146 for the two' outside air fans are set for a delay of a fewseconds only, in order to recover part of the heat used to de-ice theoutside air coils.

When fan No. 2 starts sail switch 68 will open its contacts' 145 andrelay RI will be deenergized. This will stop fan No. 1 and close valvesS.V.l and S.V.1A and open valves S.V.2 and S.V.2A. Also S.V.4 will closeto coil No. 2 and open to coil No. 1. RIB operates S.V.'2, S.V.ZA andS.V.4 only. OA fan No. 2 is energized by RZE and time delay clockcontacts 145 only on heating cycle and is operated without time delaythrough contacts RZA and R4A on cooling cycle.

Where previously the unit had been picking up heat from coil No. l theunit will now pick up heat from coil No. 2. Coil No. 1 is now receivingwarm fluid or gas from the high pressure side of the system by way ofinside air coil 14 through line 98 and line 9513 but its fan is notrunning and its louvers 66 are closed. The coil is thus not picking upheat. It is instead, being de-iced by hot gas fiowing from the highpressure side of the refrigeration system. i v

Coil No. 2 will be operated until it ices. When sufiicient ice formsswitch 68 will close due to reduced air flow through the coil toenergize RI. Then the cycle described will repeat.

The time delays 140 and 146 provide for recapture of some of the heat ofde-icing before the outside air fans start.

Normally coil No. 2 is the operating coil with No. 1 a standby coil incase de-icng of coil No. 2 is necessary. In rnild Winter weather OA coilNo. 2 will supply suflicient heat and OA coil No. l will not operateuntil ice forms on OA coil No. 2.

cooling The inside air fan is continually running (or as pointed outabove it can also be thermostatically controlled).

When the thermostat contacts 122 and 124 close the coils of relays R2,R3 and R4 are energized and the relays are operated. The compressorswitch is also closed by coil '136. Rl will be deenergized now by thesail switch contacts being opened on cooling cycle also by normal closedcontacts R4C being open on the cooling cycle.

R2A closes while RZB, R2C, RZD and RZE are opened. Both outside air fansrun (No. 2 through RzA). S.V.3 opens, as do valves S.V.lA and S.V.2A,S.V.6 and S.V.9 remain closed due to operation of relay 2, S.V.7 andS.V.S open. Valve S.V.S closes. 'Ihe inside air coil will now become theevaporator while coils 1 and 2 will act as condensers. If desired fanNo. l can be stopped or started during mild weather (low loadconditions) by a high pressure switch or manually. Both outside air fanswill continue to run even though the compress'or might stop because ofhigh head pressure.

If desired the paired compressor manifold valves which close or opensimultaneously can be wired in series. Doubling of the voltage on theseseries' wired coils would of course be necessary.

All motors, except inside air fan, stop and all solenoid coils aredeenergized when the thermostat is satisfied.

It is important to note that the equipment will automatically start onheating or cooling without manual change-over switches or attention ofany kind.

While I have shown and described a preferred form of my invention, itwill be understood that variations in details of form may be madewithout departure from the invention as defined in the appended claims.

I claim:

1. A heat pump comprising a compressor, a first heat exchanger means inseries with said compressor and a second heat exchanger means in serieswith the first heat second heat exchanger means comprising a pair ofcoil t members arranged in spaced parallel relation with one another andmeans for automatically connecting one of the latter pair andsimultaneously disconnecting the other of said pair from seriesconnection with the first mentioned heat exchanger means and saidcompressor in accordance with changes in a selected operating condition.

2. The heat pump of claim 1 wheren the last named means is sensitive toicing conditions of one of said pair of coil members, and isautomatically operable when a selected icing condition is reached toautomatically simultaneous'ly connect one of said coil members into anddisconnect the other of said coil members from, respectively, saidseries connection with the first mentioned heat eX- changer means andsaid compressor.

3. The system of claim 1 including control means comprising thermostaticmeans for automatically initiating operation of said system either as aheating or cooling system with respect to said first mentioned heatexchange' means, the last named said control means further comprisingmeans automatically operative to change said system from a heating to acooling system and from a cooling to a heating system upon a change intemperature alone; i

4. The system of claim 3 wherein said control means includes meansoperative to completely deenergize the control means whenever saidthermostatic means is inoperative.

5. The heat pump of claim 2 including fan means for directing air overone of said coil members for transfer of heat to or from the latter, inaccordance with the operation of said system, means associated with saidfan means comprising a switch sensitive to the amount of air beingdriven over the said one of said coil members and efiective upon areduction of the Volume of air delivered by said fan over the lattercoil member to disconnect the latter coil member from said system andconnect the other of said coil members into said system.

6. In a heat pump apparatus having in series a compressor and a pair ofheat exchanger means, usable alternately as evaporators and condensers,Conduit means interconnecting said pair of heat exchanger means andcompressor, one of said heat exchanger means comprsing a pair of coilmembers arranged in spaced parallel relation with one another andadapted to function as evaporator means, means for automaticallyde-icing one of said evaporator means while continuing the functioningof said heat pump apparatus through use of the other of said evaporatormeans.

7. The apparatus of claim 6 including means for automatically de-icingcomprising a sail switch means subject to the influence of the flow ofair over said one of said evaporator means and sensitive to thereduction in the flow of air and operative to effect de-icing andalternate use of said other of the latter evaporator means.

8. In a heat pump having a compressor, a first heat exchanger means anda second heat exehanger means, means for associating the first andsecond heat exchanger means in series with said compressor and forswitching automatically said connections of said compressor to said heatexchanger means to eifect alternately heating and cooling operation ofalternately first one and then the other of the means, one of said heatexchanger means including a pair of coil elements, and means foralternately switching one or the other of said coil elements into andout of operative connection with said compressor, the last named meansincluding automatic means sensible to icing conditions of said coilelements of at least one of said second heat exchanger means.

9. The heat pump of claim 8 including the latter autornatic meanscomprising a switch sensible to the flow of air by a powered fan meansover the latter element and effective upon the reduction of the flow ofair to cause said alternate switching.

10. The heat pump of claim 8 including a control circuit associated withsaid heat pump and including automatic thermostatically controlled meansfor automatically efiecting operation of said system to causealternately one or the other of said heat exchanger means to function asa heat supplying means or a heat withdrawing means.

11. The apparatus of claim 8 including a control circuit having meansincluding a timing device operative to initiate action of said systemutilizing one of said heat exchanger elements and then upon the passageof a preselected time to switch over to the other of said coil elements.

References Cited in the file of this patent UNITED STATES PATENT S2,293,532 Crane Aug. 18, 1942 2,530,440 Nussbaurn Nov. 21, 19502,581,744 Zimmerman .Tune 8, 1952 2, 726,067 Wetherbee Dec. 6, 1955

